a) Field of the Invention
The present invention relates to vehicular velocity controlling apparatus and method to follow up a preceding vehicle which is running ahead of the vehicle with an appropriate inter-vehicle distance maintained.
b) Description of the Related Art
A Japanese patent Application First Publication No. Heisei 10-272963 published on Oct. 13, 1998 exemplifies a previously proposed vehicular velocity controlling apparatus to follow up the preceding vehicle at a target inter-vehicle distance. This Japanese Patent Application First Publication corresponds to a U.S. Pat. No. 5,959,572 issued on Sep. 28, 1999.
A target relative velocity xcex94V* is calculated on the basis of an inter-vehicle distance L and a relative velocity xcex94V. The target relative velocity xcex94V* is subtracted from the vehicular velocity Vt of the preceding vehicle to derive a target vehicular velocity V*. Atarget driving force is calculated on the basis of the target vehicular velocity V* to control the vehicular velocity by means of a vehicular velocity controlling section. It is noted that the target driving force includes a target braking force since a negative value of the target driving force means the target braking force.
In the previously proposed vehicular velocity controlling apparatus, a use of a simple control system can cause the inter-vehicle distance to be converged into a target value thereof. The previously proposed vehicular velocity controlling apparatus has adopted an architecture of a control system of placing a most importance on such a convergence response characteristic on the inter-vehicle distance at a vehicular braking is effected with a large braking pressure set for a vehicular brake system when the inter-vehicle distance to the preceding vehicle becomes so short as to converge the inter-vehicle distance quickly into the target inter-vehicle distance in order to cope with an abrupt interruption of another preceding vehicle from another traffic lane to a front preceding vehicle trap area of the vehicle at the same traffic lane.
Hence, a magnitude of a braking force developed at the vehicular brake system is set in accordance with the inter-vehicle distance to the preceding vehicle. Consequently, a relatively large braking force is acted upon the vehicle at an initial stage of the braking so that a mismatch to a vehicular driver""s sense of vehicular driving would occur.
It is, therefore, an object of the present invention to provide vehicular velocity controlling apparatus and method which place a limitation on the braking force developed in the vehicular brake system when the shortened inter-vehicle distance is to be widened to match with the vehicular driver""s sense of vehicular driving.
According to one aspect of the present invention, there is provided a vehicular velocity controlling apparatus for an automotive vehicle, comprising: an inter-vehicle distancedetector to detect an inter-vehicle distance from the vehicle the a preceding vehicle which is running ahead of the vehicle; an inter-vehicle distance calculating section that calculates a target vehicular velocity to make a detected value of the inter-vehicle distance substantially, equal to a target inter-vehicle distance; a vehicular velocity detector to detect a vehicular velocity of the vehicle; and avehicular velocity controlling section that adjustably controls the vehicular velocity of the vehicle to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity, the vehicular velocity controlling section including a target braking pressure calculating section that calculates a target braking pressure for a vehicular brake system in accordance with a target deceleration variable calculated on the basis of the target vehicular velocity and the detected value of the vehicular velocity; and a target braking pressure limiter to place a limitation on a rate of increase in the target braking pressure when the target braking pressure is in excess of a predetermined braking pressure threshold value.
According to another aspect of the present invention, there is provided a vehicular velocity controlling method for an automotive vehicle, comprising: detecting an inter-vehicle distance from the vehicle to a preceding vehicle which is running ahead of the vehicle; calculating a target vehicular velocity to make a detected value of the inter-vehicle distance substantially equal to a target inter-vehicle distance; detecting a vehicular velocity of the vehicle; adjustably controlling the vehicular velocity of the vehicle to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity; calculating a target braking pressure for a vehicular brake system in accordance with a target deceleration variable calculated on the basis of the target vehicular velocity and the detected value of the vehicular velocity; and placing a limitation on a rate of increase in the target braking pressure when the target braking pressure is in excess of a predetermined braking pressure threshold value.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.